It is well known that in the electronics industry, particularly the personal computer industry, that the trend is to design products which are smaller, lighter, and more compact while maintaining or increasing power, speed, and memory capacity. In recent years, the computer industry has experienced the advent of the lap-top computer, the notebook computer, and now the palm-top computer. Although these computers are amazingly compact and lightweight, they are still incredibly powerful and fast. They are capable of running software applications that only in the recent past were able to be run on desk-top computers with large amounts of memory.
Personal computers (including desk-top, lap-top, notebook, and palm-top computers) include a mother board for controlling the operation of the computer. Personal computers are sold with a specified amount of memory, for example, 1.2 gigabytes (GB) of storage memory on a hard drive and 64 megabytes (MB) of random access memory (RAM). Many users upgrade the RAM of their computers. Accordingly, motherboards typically include standardized expansion slots in which a memory card may be inserted. The expansion slots may also receive cards for upgrading a particular function of the computer, such as cards for sounds, video, and graphics.
A dual in-line memory module (DIMM) connector is a standard industry connector for receiving a memory module. And in accordance with the "smaller-is-better" trend in the computer industry, many mother boards are equipped with only two DIMM connectors. As such, in order to install a larger amount of memory in only two DIMM connectors, higher density memory modules have been developed.
One conventional technique for increasing the storage capacity of a memory module is to double the height of the module. To do so, two rows of memory chips are mounted on the memory module, essentially doubling the capacity of the module. However, there are two primary disadvantages of such a configuration. One disadvantage is the double height. The housing of the computer and the area around the mother board both need to be sufficiently large in order to accommodate this doubled size of the expansion, which runs contrary to the small-is-better design principle. Another disadvantage lies in different trace lengths. A trace is the electrical conductor which connects the chips to the edge connector or interface portion of the module. In the double-row configuration, one row of chips has one trace length, and the other row of chips has another trace length. The trace of the further row of chips is essentially twice as long as the closer row of chips from the edge connector. Accordingly, a signal traveling to the further rows of chips take about twice as long to arrive as the signal traveling to the closer row of chips. This arrangement requires the signal delay to be eliminated, which may be done by synchronizing the signals, which is difficult and expensive to accomplish. Alternatively, the trace of the closer row of chips may be physically doubled in length so that the signals arrive at the two rows at about the same time. Either solution results in a module which is limited in speed by the double-length trace.
Another conventional technique for increasing storage capacity of a memory module is to configure the double-height arrangement discussed above with a foldable portion such as an integral flex conductor. The module may then be folded in half, thereby reducing the height essentially by two. However, this foldable configuration still suffers from the drawback of the varying trace lengths. An additional drawback is created by the folded arrangement in that vertical air circulation is restricted. The components of the module produce heat, and under normal convection the heated air would rise and be drawn out of the computer by a fan. However, the folded portion of the module retains heat between the folded sections, which may cause the module to function improperly and errant.
Accordingly, in view of the foregoing, it is an object of the present invention to provide an expansion module which overcomes the disadvantages and drawbacks associated with conventional expansion modules.
It is another object of the present invention to provide a memory module which maximizes memory per unit volume of space which the memory module occupies.
It is yet another object of the invention to provide a high-density memory module which operates at the highest speed possible.
It is yet another object of the invention to provide a multiple-layer memory module with a minimized trace length.
It is yet another object of the present invention to provide a multiple-layer memory module with substantially equal trace lengths between layers.
It is a further object of the present invention to provide a multiple-layer memory module having boards that can be readily connected and disconnected from each other.